There are different classes of offshore installations. For example, mobile offshore drilling units, floating platforms, fixed platforms, and tension legs. Each of these installations has their own applications and drawbacks.
Mobile offshore drilling units (MODU) are more susceptible, than other types of offshore structures to meteorological conditions such as winds, currents and, most importantly, waves. These meteorological conditions generate movement of the MODU that will inevitably be transferred to some extent to the drilling pipe, which is fixedly connected to the wellhead located in a fix spot on the seabed. When the drilling pipe is connected to the wellhead (e.g., for well intervention or drilling), the MODU utilizes a passive heave compensation system. When there is no drilling pipe connected (e.g., open sea drilling), the MODU utilizes an active heave compensation system.
Several motion intervention devices are known, for example, the use of motion intervention frames is a widely known technique in coiled tubing drilling activities. Therein the coiled tubing injector is attached to a frame that, generally, through the use of winches, is hung to a fixed structure; the winches are pneumatically or hydraulically controlled to follow the injector and thereby compensate for the relative movement between the injector and the pipeline to which the injector acts on. U.S. Patent Publication US20140308105A1 teaches an example of such motion intervention devices.
Prior art devices acknowledge the presence of meteorological conditions that modify the position of pipelines that are connected to the seafloor with respect to the vessel (and, therefore, of every intervention device located on such vessel) and have developed different kinds of frames to minimize the effects of the dynamic loads of the intervention devices and their movement with respect to the pipeline. Such compensating action is always performed on the intervention devices themselves (e.g., by hanging the intervention device to a constant-tension winch or by modifying the position of the intervention devices in view of the load of a wellhead so that it does not exceed a determined threshold value).
One of the major problems with the prior art systems is that during coiled tubing drilling a coiled tubing lifting frame (CTLF) is normally used. The CTLF is a massive structure that needs to be handled in an unmounted way and that is mounted below the derrick (i.e., it is normally too large to be mounted outside the derrick). The CTLF is subsequently hung from the top of the derrick and the injector is attached on the CTLF. When operations are to be performed on a pipeline (e.g. wireline operations for inspecting or maintaining the pipeline) the injector has to be lowered back to the vessel and the CTLF removed for safety reasons (i.e., it is unsafe to keep workers under a hanging structure). The operation process normally takes a long time (e.g., 4-6 hours) and can slow down and make drilling operations more expensive.
Another problem of prior art systems is taking measurements during well intervention operations. Specifically, switching between coiled tubing and wireline operations is a time consuming process. In traditional systems using a CTLF (as illustrated above) it can take 4-6 hours to remove the injector and configure wireline. The time spent changing configurations can add to the cost of the intervention operation.
Another problem of prior art systems is that operations to be performed on the drill riser (i.e., while the injector is attached to the pipeline) are typically performed by a man-rider or harnessed worker (e.g., by crane). Thus, it can be difficult to perform complex operations or to perform work between several people. Furthermore, if work is to be performed on the injector is has to be lowered to the deck of the vessel. In both of these cases, the use of prior art techniques result in a timely and risky operation.
Another problem encountered with the prior art systems, is the complexity of changing from a coiled tubing drilling to a joint-pipe drilling configuration. (e.g, to change from an injector to a top-drive). In prior art systems, the intervention frame must be reconfigured to a new weight and the injector has to be disengaged from the conduit and removed to a platform (i.e., on the vessel). The movement of such a heavy device is unsecured and the vessel is subject to movements that can damage the device. Furthermore, the change between modes requires a considerable amount of time.